This invention relates to a color display, and more particularly to an apparatus for driving a color liquid crystal display panel which has a relatively large display area, which can display a reproduced picture with a high resolution and which is suitable for use as a display incorporated in, for example, computer systems and various kinds of control apparatus.
An apparatus for driving a color liquid crystal display panel is disclosed in, for example, JP-A-59-211021. The disclosed display panel driving apparatus includes a frame memory for storing color display data temporarily. The color data of red, green and blue corresponding to individual lines of the color liquid crystal display panel respectively are then repeatedly read out from the frame memory to be supplied to the color liquid crystal display panel.
The color liquid crystal display panel used in the prior art display panel driving apparatus has a relatively large display area of, for example, 640 dots .times. 200 dots. Thus, when the color liquid crystal display panel having such a relatively large display area is to be driven for displaying a picture, the amount of display data required to display the picture increases correspondingly, and this leads to the problem that the frame memory must have an increased memory capacity.
Further, in the prior art color liquid crystal display panel driving apparatus described above, color data of red (R), green (G) and blue (B), each for displaying 640 dots, are to be supplied to the color liquid crystal display panel in one horizontal period. These display data are serially supplied as an input to a column-direction (X) signal-wire drive circuit which is connected to the color liquid crystal display panel and includes a shift register. The supplied display data are serial/parallel converted by the shift register, and the parallel display data are supplied to the column-direction signal wires from the respective bit outputs of the shift register.
The frame frequency required for the color display by the color liquid crystal display panel is dependent upon the data transfer rate of the X (signal-wire) drive circuit carrying out the serial/parallel conversion of the color data. When, for example, an X drive circuit of the type "HD66106" sold by Hitachi, Ltd. and having a maximum data transfer rate of 6 MHz is used for the serial/parallel conversion, the frame frequency f is given by the following equation (1): ##EQU1##
In the above equation (1), the second member, (640/4), of the denominator means that the unit of color data serially transferred is 4 bits, and the third member, (200.times.3), of the denominator means that three primary color lines of R, G and B constitute one color dot (line).
When the frame frequency f is only of the order of 62.5 Hz as described above, the color liquid crystal display panel encounters such problems as flickering display of a picture and degradation of the picture quality at high temperatures. That is, when the liquid crystal display panel has an active matrix structure in which an a.c. voltage is applied across the liquid crystal cells, it is required to write color data by alternate application of both the positive polarity and the negative polarity. Therefore, in such an active matrix structures, the substantial frame frequency f will be lowered to about 31 Hz which is only about 1/2 of the aforementioned frame frequency f.
JP-A-61-52631 is referenced as another prior art document related to the present invention. JP-A-61-52631 discloses a display panel driving apparatus in which a column-direction signal wire drive circuit driving column-direction signal wires of a display panel is divided into a plurality of drive circuits so as to shorten the period of time required for data writing. However, in the disclosed display panel driving apparatus, a plurality of shift registers and sample/hold circuits must be disposed in the preceding stage of the individual drive circuits, resulting in complexity of the circuit structure.